X-ray target



April 6 1926.

v ATTORNEY Patentnecl Apr. 6, 1926.

UNITED s'rA'Tl-:s PATENT oFFicE.

EABVEY C. BENTSCHLEB, OI' EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

x-RAY TARGET.

Application flled A prll 18,1921. Serial No. 461,051.

To all wlwm z't may concern.-

Be it known that I, HARVEY C. REN'rscH- LER, a citizen of the United States, and a resident of East Orange, in the county of Essex and State of New Jersey, have lnvented a new and useful Improvement 1n X- Ray Targets, of which the following is a specification.

This invention relates to X-ray apparatus and more particularly to targets employed in X-ra tubes.

An 0 ject of the invention is to provide an X-ray target which eficiently emanates 'X-rays to produce a clear and sharp shadow in an X-ray picture.

Another object of this invent1on 1s to provide a noxel X-ray target having the focal spot thereof formed of a material of high ray-radiating capacity and having the remaining portion of the target formed of a material of relatively low ray-radiatmg ability.

Another object of my inventlon is to provide a composite target for X-ray tubes in which the metals are joined in intlmate contact by sintering.

A further object of my 1nvent1on 1s to provide a process for removing the occluded gases from the materials which are to be employed in making an X-ray target while simultaneously sintering the metals together to bring the same into intimate contact.

Other robjects of the invention will be apparent from the following descriptlon.

During the development of apparatus for producing X-ray pictures, the X-ray tubes have received special consideration, and, .particularly have the targets been the subject of special attention. )ne of the accepted theories of the operation of an X-ray tube is that electrons pass from the cathode, which is sometimes designated as the negative eleetrode2 to the target, and, as a result of their impmging against the target, X- ra s are generated and radiated from the tube. The targets may be of any desired shape but the construction is of the wellknown form having an inclined surface in which is placed a small insert formed of a highly refractory metal which preferably operates as the focal spot.

Heretofore, in the operation of X-ray-apparatus, many of the resulting pictures have not been entirely satisfactory in that they did not produce a perfectly clear-cut shadow. This indistinctness is largely due to the stray rays generated by portions of the target other than the focal spot, and these rays help in dproducinfl' the cloudiness of the shadow an thus mahe an X-ray picture which is not always readily susceptible of a clear and positive diagnosis. Inasmuch as the X-ray apparatus has a ver extended use in diagnosing conditions o the VVhuman body, it is highly essential that correct deductions may be made from an examination of the X-ray pictures.

This invention will be described in connection with a Well known type of target consisting of two metals, one being an insert held within a portion of a second metal which preferably per-forms the double function of being a supporting body and a heat conductor and heat radiator Which latter feature permits a rapid dissipation of heat from the insert. For convenience 'of description, the insert will be considered as the focal spot of the target, with the Operating surface thereof formed at an angle to the major axis of the target in accordance with the usual construction of such targets.

The specific application of this invention Will be described-in relation to such materials and arrangement thereof as will produce a distinct and clear shadow in an X- ray picture.

Referring to the drawing, the figure therein illustrates an X-ray target or anode of conventional design. The target 1 is constructed of metals having highly refractory characteristics in order that they may Withstand the heat developed during the operationof the tube and may also properly conduct the heat from the insert.

In determining the materials to be employed, it is preferred that the atomic weights be considered, as it is well known in X-ray work that the ray-radiating ability of the metals bears a relation to their atomic 'weights The preferred construction of the target has the focal spot 2 formed of a metal of high ray-radiating ability and has the surrounding and supporting body 3 formed of a metal which has a relatively lowrayradiating ability. With this combination of metals, it is found that the shadow in the X- ray picture is appreciably more distinct than in pictures heretofore obtained, as the rays radiated from the supporting body are reduced to the minimum, thus redueing the stray rays Which tend to cloud the' shadow in the picture.

A preferred example of metals employed in forming Va target which produces a distinct picture may be stated as consisting of thorium and chromium; the former being the insert and focal spot and the latter being the surrounding and supporting body. Other metals or alloys, which lpreferably have'high and low atomic Weights2 respectively, may be utilized, as, for instance, uranium may be substituted for thorium, and titanium may be substituted for chroini- A target formed in accordance with the above example operates in practice to reduce the undesirable X-rays which tend only te make the picture indistinct.

The metals or alloys forming the target may be held together in aiiy desired manner. WVhcn the surrounding or supporting body is employed as a heat-radiating unit, it ist4 preferable to join the two metals in intimate contact as, for instance, by .sintering In forming a target of thorium and chromium, it is preferred to' place powdered tliorium surrounded by a substantial quantity of powdered chromium in a press and to force them together into the form of a slug or ingot. These inetals are preferably siiitered together by placing the slug in a higli-frequency vacuum furnace and Operating the same at a high temperature. Such a furnace is described and claimed in my copending application, Serial No. 430,118 filed December 13, 1920, entitled Furnaces, and assigned to the WVestingliouse Lam Company.

The vacuuin furnace a so operates to remove objectionable gases from the metals, whereby the exhausting of the X-ray tube, after the target has been assembled therein, is quickly and readily accomplished.

In some instances, it may be desirable to join the metals by otlier methods, as by casting a metal which is to act as the supporting body around a body of thorium. If desired, the surrounding body may be formed first and the insert metal east into an opening reserved therefor.

Various metals or combinations thereof may be employed in forming targets for X- ray tubes but it is to be understood that targets, such as contemplated, which reduce the number of undesirable radiated rays are considered as being within the scope of this invention, as defined in the subjoined claims.

lThat is claimed is:

1. An X-ray target having a focal spot of a material of high atomic weight surrounded by a material of low atomic weight and having a melting point above 1500 C., said materials being sintered together on their contiguous surfaces. l

huven-79 2. An X-ray target of highly refractory metals, one of said metals being adapted-to generate effective X-rays and the other metal being a poor ray-generating metal,

5. An X-ray target comprising a highly refractory material for the focal spot and a highly rcfractory material for supporting said focal material, said supporting material having low ray-radiating characteristics, said materials having their contiguous 'surfaces sintered together. p 6. An X-ray target comprising a metal of atomie weight greater than 185 for the focal spot and a supporting metal of relatively low atoniic weight and having a melting point above 1500 C., said metals being sintered together on their contiguous surfaces.

7. An X-ray target coinprising thorium for the vfocal spot of the target and chromiuni as a surrounding supporting body for said thorium, said focal spot and body being in intimate contact on their contiguous surfaces.

8. An X-ray target having a focal spot of high ray-radiating capacity and surrounding metal of relatively low ray-radiating capacity and having a meltingpoint above 1500 C., said focal spot and metal being sintered together.

9. An X-ray target having a focal spot consisting of a high ray-radiating metal and a surrounding supporting body of a relatively low ray-radiating metal and having a melting point above 1500 C., said metals beinflr sintered together at their contiguous sur aces.

10. An X-ray target having the center thereof composed of a body of high rayradiating capacity and the surrounding body of relatively low ray-radiating capacity sintered to said first body.

11. An X-ray target comprising two metals having the characteristics of high melting points and materially different rayradiating ability, said metals being sintered together at their contiguous surfaces.

12. An X-ray target composed of two metals intimatelyjoined together by sintering along their contiguous surfaces to rovide effective means for condueting eat 4'therebetweem 13. An X-ra target composed of two bodies of meta, one of said bodies being inserted in the other, said metal bodies being sintered together to form a path for the conduction of heat therebetween.

14. A target for X-ray tubes comprising a focal spot of a highly refractory metal and a body portion surrounding the same of another highly refractory metal but having a relatively low ray-radiating capacity With respect to said first metal, said metals being sintered together along their contiguoue surfaces and free from occluded gases.

15. The process of forming an X-ray target Which comprises forming a slug or ingot by pressing together two refractory metals in powder form and sintering the same.

16: The process of forming a composite X-.ray target free from occluded gases and having the metals forming the same in intimate contact, Which comprises pressmg to-4 gether a powdered refractory metal of high atomic weight and a powdered refractory metal of low atomic weight, the former metal being partially surrounded by the latter metal and sintering the metals together in a high vacuum.

In testimony Whereof, I have hereunto subscribed my name this twelfth day of April, 1921.

HARVEY o; RENTSCHLER. i 

